Messed around in Sketchup a while back and came up with this idea for a "desk" made out of foam board. The bottom tray is for holding a keyboard and trackpad, while the tray on the side is for a keypad. Since all of this is going to be held up by an ergotron arm with a weight limit of 30lbs I wanted it to be super light and still sturdy to use. The pads on the bottom of the cintiq will be held with strong double sided tape and the various pieces will be hot glued together.

If the tape ends up not sticking, i'll probably go with taking the screws out of the sides, replacing them with longer ones, and using that to support the braces on the sides and bottom.